Crease in party clothes (3-3)
I believe the answer is:
dog-ear
'crease' is the definition.
(thesaurus)
'party clothes' is the subsidiary indication.
'party' becomes 'do' (do is a kind of party).
'clothes' becomes 'gear' (I've seen this before).
'do'+'gear'='dogear'
'in' is the link.
(Other definitions for dog-ear that I've seen before include "Fold on page's corner" , "Fold down a corner (of a page)" , "Turned-over page corner" , "Hint of shabbiness" , "Corner of a page turned down to mark your place" .)